The popularity of the use of medicaments in dry powder form is increasing at least to some extent due to the search for a replacement for dispensing devices which utilize chlorofluorocarbons to deliver a pharmaceutically active compound. Chlorofluorocarbons are said to have an adverse effect on the earth's ozone layer, but the use of a chlorofluorocarbon as a propellant in a medicament dispensing device is also undesirable for other reasons. For example, some drug compounds are incompatible with chlorofluorocarbons.
The popularity of micronized dry powder medicaments is increasing even in light of their tendency to resist flow due to factors such as static conditions, humidity conditions and the effect of van der Waal's forces between the particles. Additionally, micronized, dry powder medicaments generally tend to pack into unduly large agglomerates. If the medicament is delivered to a user in unduly large agglomerates, the large agglomerates tend to impinge on the tissue at the back of the user's throat thereby preventing the medicament from reaching the user's lungs. Such impact also tends to cause an uncomfortable "gag" reflex or coughing.
The dose of a dry powder medicament that is ultimately delivered to a user should be dispersed to maximize the respirable fraction and efficacy of the medicament delivered to the user and to avoid the attendant problems associated with large agglomerates of powder. Rosskamp et al. U.S. Pat. No. 4,046,146; U.S. Pat. No. 4,811,731 to Newell et al.; U.S. Pat. No. 2,587,215 to Priestly and U.S. Pat. No. 4,524,769 to Wetterlin all describe inhalators that are powered by the user's inhalation airflow. One problem associated with user powered dispensers is that the user's capacity to generate an effective airflow may be adversely affected by an ailment such as bronchial asthma. It is believed that the powder medicament dispensers which rely upon user generated airflow tend to be inefficient, particularly when a user's capacity to generate an inhalation airflow is adversely affected by an ailment. Another problem associated with user powered dispensers is that different persons possess widely varying abilities to generate inhalation airflows. Requiring some users to generate a considerable airflow may cause discomfort.
Wetterlin U.S. Pat. No. 4,524,769 describes a device similar to a TURBOHALER.TM. dispenser which is generally available from Aktiebolaget Draco, of Lund, Sweden and has been on sale in Europe. That device includes a perforated member with a plurality of perforations for each dosage of medicament. The TURBOHALER.TM. dispenser is a user powered inhalation device and is believed to suffer from the problems associated with user powered medicament dispensers mentioned above.